The first non-enumerative framework for diagnosing path delay faults using zero suppressed binary decision diagrams is introduced. We show that fault free path delay faults with a validated non-robust test may together with fault free robustly tested faults be used to eliminate faults from the set of suspected faults. All operations are implemented by an implicit diagnosis tool based on the zero suppressed binary decision diagram. The proposed method is space and time non-enumerative as opposed to existing methods which are space and time enumerative. Experimental results on the ISCAS?85 benchmarks show that the proposed technique is on an average least three times more efficient to improve the diagnostic resolution than existing techniques.